1. Technical Field
This invention relates to digital television (DTV) receivers and, more particularly, to the use of the NTSC tuner in production DTV receivers to improve channel acquisition and reception of the ATSC tuner.
2. Background Art
Digital television (DTV) receivers in the USA use NTSC (National Television Standards Committee) encoding of the old analog channels, and ATSC (Advanced Television Standards Committee) encoding of the new digital channels. In production, most digital television receivers will have one NTSC tuner and one ATSC tuner. During reception, only one tuner is in use decoding the program; whether that tuner is the NTSC tuner or the ATSC tuner depends on whether the channel being viewed is analog or digital.
When the ATSC tuner is set to a new channel, there is a significant time delay while the ATSC tuner acquires the new channel. This is due to many reasons, one of which is that the ATSC tuner must perform channel equalization in order to receive the digital data.
When changing channels from one ATSC channel to another ATSC channel, the present invention provides a way to use the signals from the NTSC tuner to speed the acquisition and lock on to the succeeding ATSC channel. The DTV receiver contains a microprocessor which controls many aspects of the receiver operation. This microprocessor constructs and maintains a database which contains information on each television channel.
When the television receiver is not being viewed (e.g., when the viewer turns off the display), the NTSC and ATSC tuners scan various channels and update this database. Each entry in the database corresponds to a channel. These channels may be terrestrial broadcast, satellite or cable channels. The data entered in the database for each channel include such information as whether a transmitter is detected, whether it is ATSC or NTSC, what hours of the day it operates, and how strong the signal is. If the channel is an ATSC channel, then the data will also include information about best estimate of the equalization coefficients needed to optimize reception. This database may be further enhanced by a time of day and day of the week index. For example, there may be significant multipath situations which are time sensitive; e.g., a metal door being in an open position for a fixed duration of time each day, etc. Thus, a specific channel might have multiple xe2x80x9cbest equalizer coefficient setsxe2x80x9d during the day, depending on specific conditions.
When the television receiver is turned on and displaying a digital television signal, the ATSC tuner is dedicated to this selected channel. At this time, the microprocessor continuously cycles through all of the entries in the channel occupancy database. At each entry that is an ATSC channel, but not the channel currently being displayed, the microprocessor stops and tunes the NTSC tuner to this channel. When the NTSC tuner has stabilized on this channel, the microprocessor records the signal strength of the channel. This information comes from digitizing the NTSC tuner automatic gain control (AGC) voltage. The microprocessor then causes an analog-to-digital (A/D) converter to perform a large number of high speed A/D conversions on the NTSC signal. These conversions are stored in memory. After these conversions have been performed and recorded in memory, the microprocessor uses algorithms for preliminary equalizer coefficient calculations and calculates preliminary coefficients which the ATSC tuner equalizer section would use to tune in the ATSC signal. The microprocessor then makes an evaluation of whether these preliminary coefficients are likely to be better than the coefficients stored in the channel occupancy database entry for this channel. If the new coefficients are likely to cause the ATSC tuner to acquire this channel faster, then the new coefficients replace the old coefficients. If the new coefficients are not likely to speed the channel acquisition process, they are discarded. At this time, the microprocessor proceeds to the next ATSC channel entry in the database and repeats these operations. When the end of the database is reached, the microprocessor starts over at the beginning and continues cycling until the selected channel is changed by the viewer.
If the viewer changes channels to another ATSC channel, the microprocessor immediately goes to the channel occupancy database entry for the new channel. The microprocessor loads the preliminary coefficients into the ATSC equalizer section as the new frequencies are being loaded into the front end frequency synthesizers in the ATSC tuner. This procedure allows the first attempt at channel equalization to be much closer to the final value, speeding the convergence and reducing the time needed to acquire the new channel.